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DayStar Index
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DayStar Hydrogen Alpha and Calcium K-Line filters are uniquely designed to transmit a narrow section of the solar spectrum while reflecting or absorbing undesirable parasitic light. To accomplish this, white light (which is produced by a combination of colors) must be broken down into its constituent form to produce a rainbow of colors. Each color is measured in units "Angstrom" which represent 1x10-10 meters; this is represented by the symbol "Å". The human eye can discern colors within the rainbow from 3800Å in the violet, through to about 7000Å in the crimson. Within sun light, the continuous spectrum visible in white light is interrupted by a series of black bands called absorption lines. These lines are primarily created by cool absorbing gases located in the upper photosphere or chromosphere of the sun and in order to observe phenomena interacting with hydrogen or calcium, very precise optical filtration is required. The monochromator filtration technology must successfully isolate and transmit a prominent absorption line from the rest of the spectrum. The sunlight passes through a series of filter components - each is a critical component, including: an anti reflection coated optically flat window, narrow band blocking filter, an etalon window, a Fabry-Perot solid space crystal (carefully produced in house by DayStar), a second etalon window, broad band trimming filter, and another anti reflection coated optically flat window. Delivering high purity of filtration for solar observing involves new and innovative thin film coating technology. To fill this need, DayStar has developed a laser assist coating process under computerized control. This and other filtration improvements over the recent decades has made it possible to present higher quality durable components to meet the increasing needs of our customers. The DayStar solar filters are engineered to function with an energy reduction "pre filter" or an aperture stop attached on to the front of almost any telescope, while the cylindrical housing of the Hydrogen-Alpha or Calcium K-Line filter body is installed at the focuser of the telescope. The cylindrical housing of each filter is furnished with the appropriate mounting hardware and flanges to attach the system onto a telescope; optional hardware may be needed to accept visual or imaging (film, video, or integrating CCD systems) accessories. Company Seven offers a good selection of hardware with the expertise to recommend what may be appropriate for your needs.
Above: DayStar Oven Model Filter; this is the arrangement typical of the University, ATM, and Calcium K-Line series filters. Energy Rejection Pre Filter not shown here (88,930 bytes). The effective system aperture can be as large as the that of the telescope, so we at Company Seven have decided to equip our facility to study the Sun with our Astro-Physics and TeleVue refracting telescopes of up to 200mm aperture! Although for reasons of convenience and limits imposed by our local "seeing" conditions we routinely employ telescopes of only between 90mm to 155mm.
Left: The Sun as it may appear through a "White Light" Filter. Note: image not taken on same day as Hydrogen Alpha or Calcium K-Line images shown on this page (32,724 bytes). Image courtesy of NASA). Depending on the nature of the coating or metal used to make the filter the Sun may appear white, blue, yellow (as shown at left), or orange red. The features visible in a white light filter may include: 1. dark sunspots, 2. the bright faculae, and 3. granules. One can also measure the flow of material in the photosphere using the Doppler effect. These measurements reveal additional features such as supergranules as well as large scale flows and a pattern of waves and oscillations.
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DayStar Hydrogen Alpha Filters
Left: The Sun as it may appear through a Daystar Hydrogen Alpha Filter. Note: image not taken on same day as white light or Calcium K-Line images shown on this page (37,053 bytes. Image courtesy of NASA). However, when the Sun is studied through a spectrograph or a filter that is engineered to isolate the H-alpha emission, then many more features are revealed including: the chromospheric network of magnetic field elements, bright plage around sunspots, dark filaments across the disk, and prominences beyond the limb. The most commonly used portion of the spectrum for serious studies of the Sun work is in the red portion of the solar spectrum, at the line of Hydrogen a located at 6562.81Å. At its half intensity point, this line is only 1.20Å wide. A 0.5Å bandpass filter is passing only about 1/8000 of the frequency band of visible light! Providing optical filtration in this order of dimension is most demanding, and DayStar is among the few who have been able to do this consistently, and with good durability and longevity of the filter system. Our DayStar Hydrogen Alpha filter product line currently consists of three series of filters which obviously will differ one from another by modes of tuning, by bandpass, and by spectral uniformity. In making a filter selection, one should focus on technical considerations including the desired performance requirements in terms of spectral uniformity, and filter bandpass*1.
In that all interference filtering devices are sensitive to temperature changes, all DayStar University and ATM filters are designed to operate on band at a temperature above the expected ambient conditions; this nominal operating temperature is typically between 40 and 50 degrees Celsius. To reach the nominal operating temperature it is necessary to install the University and ATM filter system elements into a compact, cylindrical temperature regulated oven. The oven is fabricated for operation in either 115 volt or 220 volt AC current. The oven is regulated by a ten turn knob pot. By controlling the current flow to the oven element models can be calibrated with settings provided with each new filter produced*. This ability to vary the current also permits those models with calibrated off-band tuning and signal optimization to shift the passband by 1.0Å per 16.8 degrees F; therefore, increase the temperature for long side shifts, decrease for short side shift. And by varying the etalon temperature the observer is able to optimize contrast and engage in Doppler studies. These precision systems are extremely difficult to produce, and may create a variable delivery schedule. *Use of a dialectic coated mirror diagonal such as our Astro-Physics "Maxbright", or TeleVue "Everbrite" with heated accessories such as the DayStar University and ATM series Hydrogen-Alpha Filters will necessitate an increase of the filter operating temperature setting because the coatings of these diagonals do block infrared energy. 2. ATM series filtering systems provide wonderful imaging fidelity at an affordable cost. Informative filtergrams can be made with slight dodging in the darkroom. Smooth spectral uniformity offered by instrument quality etalons will satisfy the needs of most observers. Nominal at f/30, ( full aperture or stopped down ) with optical systems delivering an effective focal length of up to 2000mm the user will find the spectral uniformity of these filters impressive. The ATM series are available in a bandpass range of from 0.95Å to 0.50Å. The ATM series incorporate a cylindrical temperature regulated oven similar to that provided with the University series filters. If the main stay of the observing program concentrates on filtergrams and CCD imaging, then we suggest you consider the advantages of the University series. If the main desire is for visual work and taking basic filtergrams, the is an excellent choice. During the course of manufacturing a filtering unit, each is thermally tuned by a precision factory-calibrated oven to maintain proper bandpass tuning. We are constantly amazed by images delivered by these systems. We continually receive quality filtergrams taken by ATM owners that give the "big boys" a run for their money. 3. T-Scanner series filter assemblies are designed for amateur observers doing remote observations without ready access to AC power. By taking advantage of fundamental physics relating to thin film coatings, the ATM models employ an alternative method of tuning other than controlling the etalon's temperature. The tuning is achieved by tilting the filtering assembly. Tilting the filtering system shifts the bandpass towards the shorter wavelengths. By fabricating the filter a few angstroms longer than the desired observing wavelength, the observer can optimize the contrast simply by tilting the filtering system with a control screw knob. T-Scanners are fabricated to the same quality and safety standards as the University and ATM series. These filters are intended for visual work and available in a 0.80Å to 0.50Å bandpass. Because of the internal tilting mechanism, these filter utilize an aperture of 30 mm. and operate in a nominal f/30 optical system. All DayStar Hydrogen a filters provide clear and exciting images of prominence and surface phenomena. Observers concentrating on prominence work generally prefer a wider bandpass, (0.95 to 0.80Å). Those concentrating on subtle surface detail require higher contrast or ultra-narrow bandpass filter systems, ( 0.70 to 0.50Å). The most common fabrication request is for the 0.60Å models for observing in Hydrogen a. A visual representation of Hydrogen Alpha filters for different bandpass:
0.5Å Bandpass 0.6Å Bandpass 0.7Å Bandpass 0.95Å Bandpass
For a complete review of the system components, and how they function then read the instruction manual that was written by Company Seven and that is provided by us with each controller that is sold by us.
Left: Spectroheliogram of the Sun as shown through the DayStar Calcium K-Line Filter. (60,382 bytes. Image courtesy of NASA). For visual use we offer the two cavity 8.0Å -10Å square band filter. The Calcium K-Line absorption band is about ten times as wide as the H-Alpha line, so filters having bandwidths of between 1 Å to 2 Å will provide informative filtergrams. And so for applications involving filtergrams and CCD imaging, DayStar offers a single cavity University quality 2Å bandpass system. These filter systems are designed for to be used with telescopes having f20 to f30 beams transmit sufficient energy for a visual focus of the solar disk. Since the human eye's sensitivity is taxed at this end of the spectrum, the filter is engineered for use with video, film, or CCD systems. Note. These systems do not require an energy rejection prefilters for operation. Filters operate with optical systems as fast as f/20 but due to anticipated heat loads we do not generally recommend apertures larger than 80mm. At this transmitted wavelength, a 80 mm. aperture delivers <1 arc sec. resolution. The spectral uniformity and image quality delivered at the eyepiece or imaging surface is truly remarkable.
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DayStar Double Peak Polarized Filter
The core of the DayStar Double Peak Polarized Interference Filter is a solid space birefringent etalon. As a result, the completed filter exhibits orthogonal transmission modes (S and P polarizations). Filters can be fabricated as broad as 3.0Å or as narrow as 0.4Å. Peak positions are determined by the etalon thickness which can be fabricated with separations of 0.1Å to 20.0Å. All other etalon transmission peaks are eliminated by an appropriate square band blocking filter. The filter system is installed in a temperature regulated oven and one transmission mode is tuned on band while the other peak falls off band as the reference channel. A polarizing beam splitter selects the channel to be monitored. Custom DayStar Filters: DayStar filters may be custom engineered for any application requiring the precise isolation of absorption or emission spectra from 3800Å to 1.1 microns. Depending upon wavelength, half-bandwidths from 0.4Å to 10Å are available with apertures as large as 47mm for example in Cyanogen-Corona lines, Calcium (8543Å), Helium, etc. Please contact Company Seven with your requirements. |
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Contents Copyright 1994-2002 Company Seven - All Rights Reserved |
The photosphere is the visible surface of the Sun that amateur astronomers are most familiar with. this is readily observed with relatively inexpensive solar filters such as that we offer by 
The chromosphere appears as "peach fuzz" surrounding the Sun; this is an irregular layer above the Sun's photosphere where the temperature rises rapidly from 6000°C to about 20,000°C. At these higher temperatures the hydrogen emits light that gives off a deep red color (H-alpha emission). The chromosphere derives its name (color-sphere) from this phenomena. This colorful emission can also be seen in prominences that erupt and then project to beyond the limb of the sun into the blackness of space. Prominences may be safely observed by the naked eye during total solar eclipses.
Designed to reveal information about the Sun's chromosphere by examining the light emitted by ionized calcium (Ca II), the Calcium K-Line filters are centered at a band pass of 3933.7Å in the deep blue region of the solar spectrum. Observers equipped with a DayStar Calcium K-Line filter may view and image calcium plage excited by emerging, existing, or decaying sunspot groups. In Calcium K-Line, plage immersed solar active areas will appear across the entire solar disc, not just at the limb. Prominences are commonly seen in the violet light of Calcium during solar active periods.